The present invention relates to a volumetric flow measuring device, and more particularly to swirl flow type of flow meter.
The flow measuring problem has been solved, to this day, by using very diversified techniques, mechanical as well as electro-mechanical or electronic.
Amongst the best known flow-meters, may be cited the turbine flow-meters, the pressure difference measuring flow-meters, the ultrasonic flow-meters, the electromagnetic flow-meters. All the proposed solutions display at least one of the following disadvantages:
A FRICTIONAL FORCE AND WEAR DUE TO THE EXISTENCE OF MOBILE MECHANICAL PARTS; THE RESULT IS NON LINEARITY OF THE DEVICE RESPONSE DUE TO THE ABSENCE OF KNOWLEDGE ABOUT AND THE NON-STABILITY OF THE FRICTIONAL FORCES, THE LATTER MAKING THE INSTRUMENT ALSO OFTEN UNUSABLE FOR MEASURING GAS FLOWS, AS WELL AS A DECREASE OF THE PERFORMANCE AS TIME GOES DUE TO THE WEAR OF THE MOBILE MECHANICAL PARTS;
THE NECESSITY OF A STREAM FLOWING IN WELL DEFINED CONDITIONS, A MODIFICATION OF SAID CONDITIONS (TURBULENT OR LAMINAR FLOW) HAVING AN INFLUENCE, FOR INSTANCE, IN THE CASE OF A TURBINE FLOW-METER, ON THE LINEARITY OF THE DEVICE, AND THE NON-UNIFORMITY OF THE PROFILE OF THE FLOW SPEEDS IN THE DUCT OF THE MEASURING DEVICE LEADING TO IMPORTANT ERRORS IN THE DIFFERENTIAL PRESSURE MEASURING DEVICES;
LIMITATION IN THE RANGE OF USE, DEVICES OPERATING WITH PRESSURE DIFFERENCES BEING NOT USABLE FOR LOW FLOWS RATES;
HIGH INFLUENCE OF THE PROBLEM OF DEPOSITS AND CAVITATION ON THE QUALITY OF THE MEASURES;
RELATIVELY LONG RESPONSE TIME (DIFFERENTIAL PRESSURE OR TURBINE FLOW-METERS);
OUTPUT SIGNAL IN ANALOG FORM NOT VERY COMPATIBLE WITH REMOTE TRANSMISSIONS;
OPERATING DIFFICULTY, THE ULTRA-SOUND AND THE ELECTRO-MAGNETIC FLOW-METERS REQUIRING THE USE OF A COMPLICATED AND CUMBERSOME EQUIPMENT INVOLVING AN INCREASED RISK OF FAILURES, HIGHER COSTS, MORE DIFFICULT REPAIRS AND A HIGHER ENERGY CONSUMPTION;
DIFFICULTY IN EXPLOITING THE MEASURE, THE INFORMATION RELATIVE TO THE FLOW MEASURED WITH DIFFERENTIAL PRESSURE FLOW-METERS BEING OBTAINED FROM THE MEASUREMENT OF A PRESSURE DIFFICULT TO CARRY INTO EFFECT;
IMPORTANCE OF THE NATURE OF FLUID, THE USE OF AN ELECTRO-MAGNETIC FLOW-METER REQUIRING A GOOD KNOWLEDGE AND A GOOD STABILITY OF THE CONDUCTING PROPERTIES OF THE LIQUID.
In order to eliminate these disadvantages, there has been already proposed numerical devices for measuring the volumetric flow of fluid flowing through a generally tubular body, in which a swirl is generated by a swirling fluide precessing means, comprising means producing a variable frequency signal depending on the precession movement of the fluid, associated with a logic system arranged for conditioning said frequency.
The latter devices in which body the flux pressure and speed may vary periodically at all points of the wall of said body are indeed usable for any homogeneous fluid in whatever flowing conditions; they comprise no mobile mechanical parts and may guarantee a good testing stability in time; they may operate within a wide range of flow rates and they supply a numerical signal suitable for remote transmission.
But the construction of such devices is often delicate and requires a too high accuracy for the execution of the shapes. On the other hand, the form of the means producing the variable frequency signal does not always allow an optimal exploitation of its signals.